Pros
Carmax is a corporation and run like one. You get day off and vacation days. You don't have to fight for your pay like other dealers it's cut and dry you sell a car and you get paid x amount. There lots of training. Carmax has an excellent support system and really does try to make the customer happy if at all possible.
Cons
Too much training sometimes. In the name of training there is a very oppressive culture of people "managers" looking for what you're doing wrong rather than what you're doing right. Some of the cut and dry policies go against making customers happy. ie sometimes a car needs a tire or something cheap to make the customer happy and carmax won't do it because it "meets the carmax standards." Carmax would rather take the car back under the 5 day return policy than replace the tire.